1. Field of the Invention
This invention relates to an improvement in explosives, and more particularly, to an improved propellant charge that is capable of generating a large volume of gas in a short time and having especial utility in gun and cannon shells or cartridges.
2. Description of the Prior Art
Explosives used to propel projectiles from guns and cannons do not detonate. Termed propellants, they consist of uniform flakes, spheres, or hollow grains which burn with the production of gas. Gas is produced at a controlled rate, under a pressure of about 3500 kg./sq. cm. (50,000 lbs./sq. in.), while the projectile is being accelerated. The time available for gas generation is very short, being a hundredth of a second or less depending upon the velocity of the projectile and the length of the gun barrel.
Modern gun/cannon propellant is a smokeless-powder consisting essentially of nitrocellulose mixed with ethyl ether and ethyl alcohol to form a stiff dough. The practice has been to extrude the dough through dies, cut it into grains of desired length, and to dry it. Nitrocellulose is the major ingredient in single-base powder. In double-base powder, nitroglycerin, in an amount of about 7-68%, is provided in addition to the nitrocellulose.
Shells or cartridges have fixed shapes and volumes that are determined by the weapons in which they are used. Adjustment in the projectile propelling thrust must, therefore, be effected by variation in the form and formulation of the propellant that is used. Maximum mass loading of propellant per unit of available shell volume is the criterion to be met for best or proper performance.
Filling the shell with a single solid propellant grain would appear most efficiently to meet this objective. Such loading presents a problem, however, because the surface area of the propellant that is exposed to the flame upon ignition is limited and precludes good flame spreading and a sufficiently rapid generation of gas for proper propulsion of the projectile.
Most modern gun/cannon propellants take the form of long rods (Cordite), short rods (IMR powders), or flakes (Ballistite). (IMR powders are those documented in the Interim Memorandum Report of the Ballistic Research Laboratory at Aberdeen, Md.) These shapes are provided in order to enhance flame spreading, and hence, to heighten the rate of gas generation upon ignition of the propellant. The processing of these shapes, however, is costly. Additionally, maximum mass volume loading of the propellant is not achieved because of the air space between the rods and the flakes as incorporated in a shell.
It has been proposed in the prior art to provide a smokeless-powder cartridge wherein the smokeless-powder is ignited simultaneously at all points. Thus, as disclosed in U.S. Pat. No. 838,748 dated Dec. 18, 1906, and granted to Francis I. du Pont, there is provided a smokeless-powder charge in the form of a sheet and a priming charge of quick-burning material, also in the form of a sheet, superimposed one on the other and coiled within a cartridge. It is evident that such an arrangement fails to achieve maximum mass loading of the smokeless-powder, irrespective of how tightly coiled, because of the volume occupied by the priming charge of quick-burning material.
In U.S. Pat. No. 552,919, dated Jan. 14, 1896, and granted to Hudson Maxim, there is disclosed a cellular explosive charge comprising a continuous sheet of an explosive colloidal nitro compound having a multiplicity of interior widely separated non-communicating cavities. The sheet is rolled into a cylindrical form. The cavities are produced in the sheet in a number of different ways, as by forcing air into the sheet while it is in a plastic condition, placing hollow capsules or bits of sponge in the mass while viscid, and by drawing the sheet between rolls one of which is smooth and the other having projections that punch spaced rectangular depressions in one side of the sheet. When the sheet is rolled up, the depressions form spaced cavities in the resulting cylinder.
When ignited, the Maxim cylinder is said to continually break up as it is being consumed thereby to present additional surfaces to the flame for increasing the rate of consumption and causing an accelerating pressure upon the projectile. Since the cavities in each case are widely separated, the breakup during burning is unpredictable and the contribution made thereby to improving the flame spread leaves something to be desired.
In the Maxim patent, it is contemplated that granular powder may be used to fill the depressions that are punched in one side of the sheet. While this may improve the loading, it does so with a material that is less effective for the generation of gas, namely the granular material. Moreover, there is no disclosure as to how this operation would be carried out. It would appear to comprise a manual procedure that is labor intensive and costly.
There is thus a need and a demand for further improvement in propellants and particularly in their physical configuration and formulation for use in guns and cannons.